1. Field of the Invention
The present invention relates to image processing. More particularly, embodiments of the present invention relate to image processing systems for use with patient positioning devices.
2. Description of the Related Art
One application of the present invention is in the field of radiotherapy. Radiotherapy consists of projecting onto a predetermined region of a patient=s body, a radiation beam so as to destroy or eliminate tumours existing therein. Such treatment is usually carried out periodically and repeatedly. At each medical intervention, the radiation source must be positioned with respect to the patient in order to irradiate the selected region with the highest possible accuracy to avoid radiating adjacent tissue on which radiation beams would be harmful.
A fundamental problem with radiotherapy is the need to position the patient in the same position, when obtaining diagnostic images and each of the subsequent times when radiation is applied to the patient=s body. Present systems for positioning patients include various forms of systems for placing markers on the patient to enable the patient to be realigned for different applications of therapy.
Thus for example U.S. Pat. No. 5,954,647 discloses the use of a specially moulded bite plate on which LED=s are placed to enable the head of an individual to be orientated in the same position in which diagnostic images are obtained. Similarly U.S. Pat. No. 5,446,548 describes another positioning and monitoring system. The system of U.S. Pat. No. 5,446,548 involves the fixing of infra-red reflective markers on parts of a patient=s body.
Although known systems involving the tracking of markers fixed relative to the patient enable the patient=s positioning to be monitored, it is desirable to be able to determine the patient=s position more accurately to increase the effectiveness of treatment. Further, it is desirable to provide a positioning system which minimises the extra time required and the inconvenience to a patient arising from placing or fixing markers and thus reduces the stresses placed upon the patient during treatment.
To that end Vision RT Limited have developed a patient positioning system in which a three dimensional model of the surface of the patient is generated utilising a number of stereoscopic video images of the patient. The video images are processed to generate a three dimensional model which is rapidly updated to account for movement and any changes in the position of the patient. This patient positioning system is described in detail in Vision RT Limited's co-pending U.S. patent application Ser. No. 10/516400 which is hereby incorporated by reference. It is however, desirable to improve further the accuracy with which three dimensional models of patients can be generated and utilised to position a patient relative to a therapeutic apparatus such as a radio therapy apparatus.